Western Australia in autumn 2013: Warm days and nights

Rainfall

Rainfall during autumn 2013 was above average across large parts of eastern
and southern WA. A particulary wet season was observed in the southern Goldfields,
western Eucla, and Southeast Coastal and some sites recording their wettest
autumn on record. The remaining Southwest Land Division (SWLD) saw generally
near average rainfall during autumn, with small patches of above average rainfall
scattered across the Division and a small area below average in the inland South
Coastal and Great Southern. The remainder of the state was generally near average,
apart from patches of below average rainfall in the Pilbara and Gascoyne.

Averaged across WA as a whole, autumn 2013 rainfall was near average for the
State, with near average rainfall in March and April followed by above average
rainfall in May. The Lower Southwest (southwest of a line from Jurien Bay to
Bremer Bay) also saw near average rainfall, with the 12th wettest March followed
by below average rainfall in April, and a near average May. For the SWLD as
a whole, autumn rainfall was above average.

The passage of ex-tropical cyclone Rusty through central parts of the
State at the start of March, after crossing the coast east of Port Hedland on
27 February, brought heavy rainfall to parts of the Southern Interior and Goldfields.
Several sites in the western Southern Interior and Goldfields observed their
wettest autumn day on record on the 1st and 2nd, including Glen-Ayle (Southern
Interior) with a daily total of 177.5 mm in the 24 hours to 9am on the
1st. The SWLD received notable autumn rainfall on 14 May
as a result of a nearby middle level trough. Widespread falls between 30 mm
and 50 mm were reported in the Lower West and Great Southern, whilst Chesalon
in the western Southeast Coastal reported 63.2 mm in the 24 hours to 9am on
the 15th, its highest autumn daily fall in 48 years of record.

A strong cold front and deep pre-frontal trough combined to produce widespread
moderate rainfall in the SWLD and neighbouring Gascoyne between 25 and 27 March.
Widespread falls between 20 and 40 mm were reported, whilst Desert Fringe in
the southeast Great Southern recorded 80.0 mm on the 26th, its highest autumn
daily fall in 34 years of record and the highest daily fall reported during
the event.

A band of middle level cloud moved across the southern half of WA between 17
and 19 April, bringing rain and isolated thunderstorms with some moderate falls
mainly in the 10 mm to 35 mm range. A thunderstorm produced a heavy
downpour at Mount William (Southwest) during the evening of the 17th with 16.0
mm recorded in the 10 minute period ending 2125 WST, which is considered a one
in ten year event. Lorinna in the Southeast Coastal observed 61.2 mm in the
24 hours to 9am on the 18th, its wettest autumn day in 42 years of record.

Numerous unseasonal rainfall events occurred across northern WA in May 2013.
Rain and thunderstorms were common across the Kimberley from 12 to 24 May with
some heavy falls reported. Very heavy rainfall
in excess of 150 mm was reported on the northern Dampier Penninsula on the 19th
and 20th as Cygnet Bay observed 155.4 mm in the 24 hours to 9am on the 21st,
its wettest May day in 50 years of record, and Lombadina Airstrip reported 182.5
mm, the highest daily rainfall total in WA for autumn 2013.
Cape Leveque recorded 157.7 mm on the 21st, which contributed significantly
to its autumn total rainfall of 409.9 mm, the highest autumn 2013 total rainfall
in WA.

Maximum temperature

Mean daily maximum temperatures during autumn 2013 were above to very much
above average throughout much of WA, with an area of highest on record in the
eastern Eucla. The only areas to experience near average daytime maxima were
parts of the southeastern SWLD, southern Goldfields, far west Pilbara, east
Pilbara, far south Kimberley, and northern Northern Interior. Maximum temperatures
were up to 2 °C above average through much of central and eastern WA,
grading to up to 4 °C above average in the eastern Eucla.

When averaged across the state, the mean maximum temperature for autumn 2013
was above average, primarily due to WA recording its third warmest April on
record along with a near average March and May. The Lower Southwest (southwest
of a line from Jurien Bay to Bremer Bay) also recorded an above average maximum
temperature when averaged across the season, with a cooler than normal March
combining with the third warmest April and a near average May.

Cold days were observed through the SWLD on the last two days of May as a strong
cold front and a pool of cold air moved over the area. Maximum temperatures
were particularly low on the 30th, when Manjimup and Jacup observed just 9.4 °C,
the lowest maxima in WA for the season. It was Jacup's lowest autumn maximum
temperature in 20 years of record, whilst Manjimup equalled its lowest autumn
maximum temperature in its 54 years of record. Ongerup registered its lowest
maximum temperature for autumn in 46 years of record with 9.5 °C, and
Wagin equalled its record low autumn maximum in 41 years with 10.6 °C.

Minimum temperature

Mean daily minimum temperatures during autumn 2013 were above to very much
above average throughout virtually all of the State, with areas of highest on
record in the Eucla and adjacent parts of the Southeast Coastal. Esperance in
the Southeast Coastal observed its warmest autumn in 43 years of record, with
a mean minimum temperature of 14.4 °C, breaking the previous record
of 13.9 °C set in 2005. The only areas to experience near average overnight
minima were small parts of the Kimberley and central WA. Minimum temperatures
were up to 2 °C above average through much of southern and eastern
WA, grading to up to 4 °C above average in the Eucla.

When averaged across the state, the mean minimum temperature for autumn 2013
ranked as 7th highest on record since comparable records commenced in 1910,
with an above average March followed by the 5th warmest April and 9th warmest
May on record. The Lower Southwest (southwest of a line from Jurien Bay to Bremer
Bay) also recorded its 7th warmest autumn on record, with a near average March,
the warmest April since comparable records commenced in 1910, and an above average
May.

Light winds and partly cloudy conditions after a hot day on 7 March resulted
in very warm overnight temperatures in the Pilbara and Gascoyne. Gascoyne Junction
observed a minimum of 32.1 °C on the 8th, the warmest night in WA during
autumn 2013, and an autumn record in 43 years for the site. Cloudy conditions
and warm northerly winds on 26 March resulted in Eucla observing its warmest
autumn overnight temperature in 54 years of record with a minimum of 27.1 °C.

A cold morning was experienced across the SWLD on the last day of May 2013,
with mimimum temperatures dropping to below 5 °C at numerous sites
and a number of sites registering sub-zero temperatures. A minimum of 3.3 °C
at Lancelin (Lower West) on the 31st was its lowest autumn temperature in 47
years of record.

Notes

A Seasonal Climate Summary is prepared to list the main features of the weather in Western Australia using the most timely and accurate information available on the date of publication; it will generally not be updated. Later information, including data that has had greater opportunity for quality control, will be presented in the Monthly Weather Review, usually published in the fourth week of the month.

This statement has been prepared based on information available at
3 pm on Monday 3 June 2013.
Some checks have been made on the data, but it is possible that results will change
as new information becomes available.

Averages are long-term means based on observations from
all available years of record, which vary widely from site to site.
They are not shown for sites with less than 10 years of record, as they cannot then be calculated reliably.
The median
is sometimes more representative than the
mean
of long-term average rain.

The Rank indicates how rainfall this time compares with the climate record for the site,
based on the
decile ranking
(very low rainfall is in decile 1, low in decile 2 or 3,
average in decile 4 to 7, high in decile 8 or 9
and very high is in decile 10).
The Fraction of average shows how much rain has fallen this time as a
percentage of the long-term mean.

The ACORN-SAT dataset
is being used for temperature area averages from December 2012 onwards.
The major change from earlier datasets is that the ACORN-SAT dataset commences in 1910, rather than 1950,
and hence rankings are calculated using a larger set of years.